In recent years, semiconductor industry typical in LSIs is increasing rapidly. In semiconductor elements of 64 Mbit DRAMs and subsequent ones, the higher the integration, reliability and functionality become, the higher accuracy is demanded for microfabrication technology. With such higher densification of an integrated circuit, a width of metal interconnection formed essentially of Al or Cu is becoming ¼μm or less.
On the other hand, to operate an integrated circuit at a high speed, it is indispensable to reduce resistance of an Al interconnection or a Cu interconnection. In the existing interconnection structure, the interconnection resistance is generally reduced due to an increase in the height of the interconnection. However, in semiconductor devices where further higher integration and densification are achieved, an existing stacking structure causes a poor coverage of an insulating film formed on the interconnection, resulting naturally in a deterioration of yield. Accordingly, the interconnection technology of the devices itself is demanded to improve.
Accordingly, dual damascene (DD) interconnection technology different from the existing one is under study. In the DD interconnection technology, first, on a substrate film thereon an interconnection trench is previously formed, metal essentially consisting of Al or Cu that is interconnection material is deposited by use of sputtering method or CVD method to form a film. Then, after letting fill the interconnection metal in the trench due to heat treatment (reflow), an excess of the interconnection metal is removed by use of CMP (Chemical Mechanical Polishing) method or the like.
Here, in a DD interconnection structure, how to excellently fill Al or the like in the interconnection trench is of importance. As filling technology, the aforementioned reflow technology or the like can be applied. As a film improving reflow characteristic of Al (liner film), a Ti film is generally used. However, the Ti film, in the step of reflow, reacts with Al to form Al3Ti compound to result in a remarkable increase of the interconnection resistance.
In view of these, the liner materials to Al in the place of Ti are variously under study. Among these, Nb in particular is reported to be effective in use. Nb, in comparison with Ti, can reduce the interconnection resistance and improve reflow characteristics of Al.
When considering an application in the next generation semiconductor memories such as DRAMs of an integration rate of 256 Mbit or 1 Gbit or more, resistivity of an interconnection film is demanded to be 4 μΩcm or less, for instance. However, when with a Nb film deposited by use of an existing Nb target as the liner material, thereon an Al film or Al alloy film is deposited to form an Al interconnection film, it is difficult to suppress the resistivity to 4 μΩcm or less with reproducibility.
In addition, though being necessary to suppress admixture of dust in the interconnection film as much as possible, in the existing Nb target, there is a problem that giant dust such as exceeding 1 μm for instance occurs suddenly. As a result, product yield of the semiconductor devices remarkably deteriorates.
As mentioned above, in the Al interconnection film having the Nb liner film formed by use of the existing Nb target, the resistivity of for instance 4 μΩcm or less that is demanded for the DRAMs of 256 Mbit or 1 Gbit or more can not be satisfied sufficiently and with reproducibility. Further, during deposition of the Nb liner film, the giant dust suddenly occurs to result in a decrease of the product yield of the semiconductor devices. Thus, the existing Nb target faces a difficulty in applying in the next generation semiconductor memories or the like.
An object of the present invention is to provide a sputtering target that, in applying the DD interconnection technology to form an Al interconnection film, enables to heighten electrical characteristics and quality of the Nb film as liner material of the Al film. In specific, the object is to provide a sputtering target that enables to obtain with reproducibility a Nb film capable of suppressing the resistivity of an Al interconnection film to for instance 4 μΩcm or less. In addition, another object is to provide a sputtering target enabling to suppress a sudden occurrence of the giant dust and to improve the product yield of Nb films.